The present invention relates to automatic vehicle exterior light control systems. More specifically, the present invention relates to light source detection and categorization systems for use with automatic vehicle exterior light control.
Automatic exterior light control systems for vehicles have been developed that utilize various light sensors and, or, an array of sensors (commonly referred to as an array of xe2x80x9cpixelsxe2x80x9d or xe2x80x9cpixel arraysxe2x80x9d) to control the state of external lights of a controlled vehicle. These systems may, for example, be employed to detect the headlights of oncoming vehicles and the taillights of leading vehicles and to dim, or switch, the high beam headlights of a controlled vehicle off when headlights or taillights are detected. An automatic exterior light control system is described in detail in commonly assigned U.S. patent application Ser. No. 09/800,460, to Stam et al., the disclosure of which is incorporated herein by reference. Automatic exterior light control systems employing a pixel array are capable of capturing images of the scene forward of the controlled vehicle and base the exterior light control decisions upon various aspects of the captured images.
Automatic exterior light control systems are required to accurately distinguish various features of a given scene to separately categorize scenarios which require control activity from scenarios which do not. For example, taillights of leading vehicles have to be distinguished from red traffic lights and red roadside reflectors. When the high beams of the controlled vehicle are on, it is desirous to automatically switch to low beams, or dim the high beams, when taillights of leading vehicles are detected. Conversely, detection of red traffic lights and red roadside reflectors should not invoke switching, or dimming, of the controlled vehicle""s high beams.
A significant feature of sensors and optical systems for exterior light control relates to their ability to detect and accurately measure the brightness and color of small, distant, light sources. In order to perform satisfactorily, an optical system for such an application is preferably capable of identifying taillights of leading vehicles at distances of at least 100 meters and most preferably over 200 meters.
The resolution of an optical system is an important feature in accurately distinguishing between various objects within a given scene. The center-to-center distance between adjacent pixels of a pixel array is commonly referred to as the xe2x80x9cpixel pitch.xe2x80x9d The given pixel pitch and the associated lens system design are two significant components in deriving the corresponding optical system resolution.
A typical taillight is about 10 cm in diameter, or less. The angle subtended by such a taillight, at 200 meters, when projected upon a sensor, or pixel array, of a sharply focused optical system, is approximately 0.03xc2x0. Typical pixel arrays, with associated lens systems for use in exterior vehicle light control applications, are designed to image 0.1xc2x0-0.5xc2x0 horizontally and vertically per pixel. Consequently, with known optical systems, a projection of a taillight onto a typical pixel array may be of a size substantially less than that of one pixel pitch.
In known automatic vehicle exterior light control systems, the associated small size of projected, distant, light sources severely impairs the ability of the system to accurately determine the color and brightness of the corresponding light source. This is due largely to the fact that known sensors, and individual sensors of known pixel arrays, have a non-uniform response; depending upon the region of the pixel where light is incident, the sensitivity of the pixel will vary. For example, light falling on a transistor, or other structure that does not absorb photons, within the pixel will not be absorbed at all and thus will not be detected. Additionally, the given pixel may be more or less sensitive to light falling on various regions depending on the distance between the point where a photon is absorbed and the corresponding collection node to which the generated electrons must diffuse.
U.S. Pat. No. 6,005,619, to Fossum, titled xe2x80x9cQuantum Efficiency Improvements in Active Pixel Sensorsxe2x80x9d and incorporated in its entirety herein by reference, describes the pixel structure of a photogate active pixel for use in a CMOS pixel array suitable for use in a vehicle exterior light control system. FIG. 26 depicts a group of four pixels from the Fossum device. As is readily seen from FIG. 26, there are several different materials and structures that form each pixel represented by 2600, 2602, 2604 and 2606. Thus, the sensitivity of the pixel to incident light rays varies depending upon the particular region of the pixel onto which photons are incident. As discussed above, micro-lenses may be employed to focus light rays on the most sensitive area of the pixel.
Pixel non-uniformity becomes especially problematic when attempting to determine the color and brightness of small, distant, light sources. For example, the optical system described in U.S. patent application Ser. No. 09/800,460 utilizes a lens system assembly with first and second lens systems. The first lens system projects the associated field of view onto one half of the associated pixel array and the second lens system projects substantially the same field of view onto the other half of the pixel array. A red spectral filter is placed in the optical system such that the light rays projected by the first lens system are red filtered. By comparing light rays projected through the red spectral filter with the unfiltered, or complementary filtered, light rays, a relative red color of each object within the field of view is determined. When the light sources are small, distant, sources, minor misalignment of the first lens system relative to the second lens system can cause significant error in the relative color measurement. The distant light source projected by the red spectral filtering lens system may be incident onto a sensitive region of a pixel, while the light source may be projected onto an insensitive region by the second lens system, causing an erroneously high redness value. In a subsequent image, the above scenario may be reversed causing an erroneously low redness value to be attributed to the light source. Consequently, distant taillight detection of known systems is less than satisfactory in certain scenarios.
Therefore, there remains a need in the art of automatic vehicle exterior light control systems for an optical system capable of more accurately detecting the brightness and color of small, distant, light sources.
According to a first embodiment of the present invention, a lens system is provided that projects light rays emitted by a small, distant, light source onto a sensor, or pixel array, such that the projected light rays substantially cover at least one entire sensor, or at least one pixel pitch, respectively. The optical system in accordance with this first embodiment comprises a pixel array with an associated Nyquist frequency limit. The optical system has an associated spatial frequency cutoff. In the preferred optical system, the spatial frequency cutoff is less than, or equal to, the Nyquist frequency limit of the pixel array.
In another embodiment of the present invention, micro-lenses are placed proximate each pixel. Each micro-lens projects the corresponding incident light rays such that they are focused upon the most sensitive portion of the given pixel. In optical systems that employ a single sensor, or individual sensors not grouped into an array, it is preferred to use micro-lenses on each sensor.
As another alternative to the preceding embodiments, a light ray scattering film material is superimposed between the lens system assembly and the pixel array, or is integrated into the lens system assembly. Light rays projected by the lens system assembly toward the sensor, or pixel array, are scattered such that the projected light rays are incident more uniformly across the individual pixels.
In yet another embodiment of the present invention, spectral filtering material is incorporated into the optical system such that light rays in various spectral bands can be accurately categorized by color. Thereby, for example, red light sources can be distinguished from white light sources. Particular embodiments of the present invention are capable of discerning amongst light sources throughout the visible spectrum. In yet other embodiments, ultra-violet and infrared light rays are filtered and prevented from being projected onto the sensor, or pixel array. Preferably, the spectral filter material is a pigment, as opposed to a dye.
In yet another embodiment of the present invention, an optical system is provided with a pixel array having various spectral band filter material on individual pixels. In this embodiment, an optical system having a polychromatic modulation transfer function that first drops to exe2x88x921 at a spatial frequency less than, or equal to, the reciprocal of the minimum center-to-center distance between any two similarly filtered pixels is preferred.
In one embodiment of the present invention, various external vehicle lights are used, such as high intensity discharge (HID), tungsten-halogen and blue enhanced halogen, to provide greater ability to distinguish reflections from various roadside reflectors and signs from headlights of on coming vehicles and taillights of leading vehicles. Particular spectral filter material is employed in combination with the external vehicle lights to produce desired results.
In a further embodiment of the present invention, a method of manufacturing an optical system is provided which insures that the lens system assembly is fixed proximate the sensor, or pixel array, in a precise position. An encapsulate block is transfer molded over the pixel array such that the encapsulate block is fixed to the associated circuit board. The encapsulate block provides an attachment surface for placement of the lens system assembly. A precision lens system placement machine is employed to move the pixel array relative to the lens system assembly; it is preferred to have the lens system assembly fixed in space with respect to a target and move the pixel array relative thereto, however, the pixel array may be fixed in space relative the target and the lens system assembly would be moved relative thereto. At the point the target is projected upon the pixel array as desired, the lens system assembly is fixed relative the pixel array preferably utilizing an ultra-violet light curable epoxy, or other adhesive.
In another embodiment of the manufacturing method of the present invention, a precision transfer molding apparatus is employed to transfer mold a lens system assembly proximate the pixel array. Molding the lens system assembly and the encapsulate block in one step simplifies the manufacturing method and results in lower cost.
In yet another embodiment of the manufacturing method of the present invention, a precision transfer molding apparatus is employed to transfer mold an encapsulate block with a precision lens system assembly mounting structure. A lens system assembly is provided with a mating mounting structure such that the lens system assembly can be xe2x80x9csnapxe2x80x9d fit into place. This manufacturing method provides for ease in lens system assembly replacement.
The preferred lens system is molded of polycarbonate to withstand the potentially high temperatures to which the optical system may be exposed in the automotive environment. The preferred transfer molded encapsulate block, or encapsulate block and lens when molded in combination, is formed from an epoxy material with low thermal expansion and high temperature stability to ensure that the optical system can withstand the automotive environment.
The features and advantages of the present invention will become readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying figures and appended claims.